The present invention relates to an improved tone detection system and corresponding method. The present invention is more particularly directed toward incorporation with a voice message answering system.
In the prior art, the utilization of dual tone multi-frequency (DTMF) control signals is well known. In particular, a so-called touch tone pushbutton keyboard on a standard telephone is utilized to enable a user to establish communications by the appropriate depressing of the keys. The pressing of any key will enable a pair of DTMF control signals which represent audio frequencies that correspond to a particular number. In the United States, these "numbers" include 0-9, #, * and, in military applications, four other codes.
In applications such as for a voice message answering system, (DTMF) signals are utilized not only for establishing communications but in addition to provide control for appropriate message switching, message playback, and the like. They also are used to input certain data in reply to prompts or for other reasons.
In such an application, it is quite important that the DTMF tones be accurately detected in order to provide proper responses to the specified commands.
DTMF tone detection systems have typically been designed to operate with very low levels of noise on the line. However, voice store and forward systems require that the DTMF tones be detected while voice is playing over the line. For instance, if a user of such a voice store and forward system is "calling in" to his particular system, he may be listening to messages that have been recorded into the system and while at the same time he may decide to either speed up the playback of the messages, make them louder, or go on to other messages. This can result in the user inputting DTMF control signals into the system while at the same time voice message signals are being played out of the system onto a telephone line to the user's location.
A problem with such voice store and forward systems is that those systems require the DTMF tones be detected while voice is playing over the line. Conventional tone detection systems are not well suited for this. Given an amount of time, most voices will falsely trigger a DTMF tone detection system (called "talk-off"). Most tone detection systems can be desensitized to prevent such talk-off. However, this usually results in the DTMF tone detection system missing the detection of a significant percentage of tones even when they are present.
The resulting consequence of the foregoing is that the command or control signals can be misinterpreted or not recognized at all, which would result frequently in a specified command being ignored or misinterpreted entirely.
The deficiencies of prior art systems as set forth above are quite evident. It is therefore an objective of the present invention to provide an improved tone detection system and corresponding method for use in telephone systems and more particularly for use in voice message store and forward systems. However, the invention has application anywhere where tone detection must be optimized with high background noise.